Sammalvuori Metro Depot storage hall. Picture: M. Alantie/LänsiMetro


Construction of the Sammalvuori metro depot in Espoo, Finland is part of the second phase of the western expansion of Helsinki metro. In addition to the depot, the phase involves the construction of five new stations and seven kilometres of track. The depot is constructed due to the need for an increased number of trains and will serve the entire metro network, not only its western part.

The contractor for the Sammalvuori depot of the West Metro comprises the Sammalvuori Consortium, which is comprised of the companies Kalliorakennus-Yhtiöt Oy, EM Pekkinen Oy, TerraWise and Aro Systems. TKF supplied four power factor correctors for the depot.

Work on the Sammalvuori depot began in May 2016. Construction engineering work for the contract will be completed in 2020. The contract includes the design, excavation and complete construction of the Sammalvuori metro depot.

In addition to technical facilities, the depot includes personnel facilities, garage and a storage hall the size of eight football fields and large enough to fit 20 trains and their cars.

Sammalvuori Metro Depot construction site. Picture: LänsiMetro


In terms of building services engineering, the technical facilities for power, air conditioning and the metro’s electrification system are situated in the connecting hallways 5-1. The hallways link the garage and the storage hall together. There are two exit shafts that also serve as smoke exhausts and emergency exits.

Around 30 to 45 people work on the depot during the building services engineering phase. Project Manager Joni Muttilainen is responsible for Aro Systems’ share of project management at Sammalvuori Depot. He started on the project about a year ago and is set to continue on the job for another year. The work is responsible and requires delegation and problem-solving skills.

The depot’s complex main power system consists of electrical systems used to service the metro, as well as technical building electrical systems, including lighting, socket outlet centres, smoke extraction and reserve power systems.

At the depot, reserve power forms a large part of electricity supply. For example, around one third of all lighting can be powered by the reserve power system. The depot is also equipped with an extensive fire alarm system. The system allows the location of a fire to be pinpointed based on heat detection. The need for power factor correction (PFC) is increased by the high amount of HVAC equipment.

The main power supply system has four transformers and main switchboards. Reactive power at the switchboards is compensated with power factor correctors supplied by TKF. The power factor correctors operate alongside the switchboards to measure power factor correction needs and produce the needed amount of reactive power for any load situation. The power factor correctors consist of four 200-kvar detuned filter capacitor banks that were installed at the same time as the switchboards.

The PFC capacitor banks were connected some months back, and will be commissioned once the depot obtains grid connection. Commissioning is simple, as TKF has supplied the correctors with a preconfigured controller that serves as the equipment’s brain. When power is turned on, the power factor correctors activate automatically. TKF carries out factory tests before the installation of equipment. Once the devices are commissioned, all steps will be re-tested manually. After this, the depot technicians will continue to monitor the equipment for some months.

Teemu Lindgren from TKF (Left) and Joni Muttilainen from Aro Systems and a detuned capacitor bank by TKF.


Aro Systems is a longstanding partner of TKF. Aro Systems uses a handful of selected suppliers with guaranteed product quality. At the beginning of a project, requests for quotation are sent to selected suppliers before a final decision is made. The qualities of a good supplier include quality, schedule, price and service.

“TKF delivered the products on time, and project management at TKF was on top of things during all steps of the project. Our collaboration was smooth and effortless,” says Joni Muttilainen.


Four TKF detuned filter capacitor banks
Type TKF-E200 / 2 x 12.5 + 25 + 3 x 50 / 400 – 50 – 189
Power 200 kvar
Compensation steps 2 x 12.5 kvar + 25 kvar + 3×50 kvar
400 V, 50 Hz
Tuning frequency 189 Hz
600 mm x 600 mm x 2,000 mm (w x d x h)
320 kg


Founded as Sähkö-Aro by Pentti Aro in 1954. The first office was located in Oulunkylä, Helsinki, in the basement of a suburban house. Initially, the company made electrical work for single-family homes. Over the years, the family-owned business has grown and expanded to Tampere and Oulu. Today, Aro Systems Oy is one of the largest technical building services providers in Finland for electrical, telecom, IT system and HVAC installation work and maintenance. At Sammalvuori Depot, Aro Systems Oy is responsible for all aspects of technical building services design for the consortium, including electrification, HVAC, automation and project management. Today, Aro Systems employs some 300 industry professionals.



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